The present invention relates to an exposure control system for a photographic camera of the type employing both a scanning blade shutter and a quench-type strobe, in general, and to a manually operable trim system for electronically controlling the aperture form by said shutter and the strobe light levels in such a camera, in particular.
Automatic exposure control systems have been incorporated within various amateur cameras for simplifying their operation by minimizing the pre-exposure adjustments to be made by a camera operator. These exposure control systems function to automatically regulate the exposure parameters for a given scene. Generally, the exposure control systems are designed for use over a wide range of scene lighting conditions.
Exposure control systems embodying scanning shutter blade elements which operate to vary the exposure aperture areas with time during an exposure interval are well known as indicated by U.S. Pat. No. 3,942,183 entitled "Camera with Pivoting Blades", by G. WHITESIDE, issued Mar. 2, 1976, in common assignment herewith. Such scanning shutter blade mechanisms generally include a pair of counter-reciprocating shutter blade elements, each having a primary aperture that transverses the optical axis of the camera during the exposure interval. The primary apertures are shaped so that upon overlying one another during counter movement of the blades, there is defined an effective exposure aperture value which increases to a maximum value in a determinate period of time.
Exposure control is provided by a pair of secondary photocell apertures and respective shutter blade elements which admit scene light to a photoresponsive element in correspondence with the scene light admitted to the focal plane during shutter blade movement through an exposure cycle. The output from the photoresponsive element is directed to an integration circuit which triggers upon reaching an integration level corresponding to a desired exposure value to terminate the exposure interval by returning the shutter blade elements back to their initial scene light blocking position.
Such exposure control systems may be utilized with a source of artificial illumination such as an electronic flash to provide artificial illumination not only during conditions of low ambient scene light intensity, but also under conditions of high ambient scene light intensity wherein it becomes desirable to provide the artificial illumination to fill-in the photographic subject against a partly lit scene as disclosed in U.S. Pat. No. 4,023,187, entitled "Exposure Control System with Fill Flash Race Condition", by E. SHENK, issued May 10, 1977, in common assignment herewith.
Since a large majority of amateur pictures are taken within the range of light levels to which the control system is suited, well-exposed photographs are obtained. However, the camera operater may wish to take a photograph which is lightened or darkened to his personal taste, or may wish to accommodate for unusual lighting effects such as backlighting, highlights or the like. In order to adjust the automatic exposure control system for such unusual scenes or effects, a lighten-darken trim is provided. These trim systems provide the user with a manual one-half to one stop optional exposure adjustment above or below the exposure value otherwise established automatically. Ideally, such trim control should be provided with only one manually adjustable component for ambient and artificial light level control. Should a dual trim system for ambient and artifical light (flash) modes be provided having more than one control element, a camera operator may become confused or overlook a requirement for providing trim control for that mode of operation which he is currently using.
In one trim control mechanism disclosed in U.S. Pat. No. 4,209,243, issued June 24, 1982, to B. JOHNSON and G. WHITESIDE, the amount of scene light admitted to the focal plane of a camera is dependent upon the amount of light passing from the scene to a photoresponsive element through a variable density filter slidably mounted on the camera body that varies the amount of scene light "seen" by said photoresponsive element. Normal exposure of photographic film in the camera will result when a medial density portion of the filter is positioned in front of the cell. Correspondingly, the exposure control system may be trimmed to either an underexposure mode upon movement of the slide to reduce the filter density and thus increase the light "seen" by the cell to a value above that indicated for normal exposure, or to an overexposure mode by moving the slide in the opposite direction to increse filter density and thus reduce the amount of light "seen" by the cell to a value below that which would pass the filter for normal exposure. However, because of the degree of precision required for an exposure control system, the limitations on the space available for the overall exposure control system and the importance of the trim mechanism to overall camera effectiveness, there is a need for structural simplicity, reliability and manufacturing cost effectiveness in trim mechanisms of this type. A trim control employing a slidable filter and photosensitive element combination does not adequately satisfy these requirements.
It is a primary object of the present invention, therefore, to provide an electronic trim control for a photographic camera that is structurally simple, reliable and cost effective.
It is another object of the present invention to provide an electronic trim control for a photographic camera of the type having a quench-type strobe, a scanning blade shutter and means for sensing ambient and artificial scene light.
It is a further object of the present invention to provide an electronic trim control for a photographic camera of the type having a quench-type strobe, a scanning blade shutter and a pair of scene light sensing photosensitive elements for establishing distinct signals representative of ambient and artificial scene light levels.
Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.